The HRAS gene (11p15.5), which encodes the HRAS protein (189 amino acids; 21,298 Da), with GTP-ase activity, acquires mutations in Costello syndrome and in several tumor types, such as melanomas, follicular thyroid cancers, bladder cancers, oral squamous cell carcinomas [37,38], and sparsely in certain appendiceal cancers: mucinous adenocarcinomas of the appendix and appendiceal adenocarcinomas, especially in appendiceal goblet cell adenocarcinomas [9]. This evidence concerns the gene HRAS and Costello syndrome.